Regarding point 4, I don't think the rotting flowers smell is supposed to be Hades. I do think it's one of the other gods influencing Hermes into madness, though, since the MC pushes back the smell with with his power in the realm, a power which is supposed to be sovereign over other gods except the Overseer (sort of). If Hermes is the only god allowed in, possessing him or intentionally driving him to madness can give you influence in the hotel to enact your plots. I also think it's not just the general god madness that seems to come from diminishing worshippers (source: the Tapir God if you get him his pelt back, and the 'old man' who we already know is another god and very far gone), but I'm not sold on who the flowers are yet. It's important to note that while Hermes, Hades, and Hestia are most certainly on Asterion's side, any of the other gods could've shifted either in or out of his favor after all of this time. I wouldn't put this past Aphrodite if she got swayed against Asterion for some reason.